In this task, you're given a context passage, followed by a question that needs to be answered. Based on the paragraph, you must write unambiguous answers to the questions and your answer must refer to a specific phrase from the paragraph. If multiple answers seem to exist, write the answer that is the most plausible.

Continuing our look at the presidential candidates , today we look at the hot button issue of the economy . This is a long one , so grab a cold drink and settle in . " John McCain has a comprehensive economic plan that will create millions of good American jobs , ensure our nation's energy security , get the government's budget and spending practices in order , and bring relief to American consumers . " " I believe that America's free market has been the engine of America's great progress . It's created a prosperity that is the envy of the world . It's led to a standard of living unmatched in history . 
Question: What has led to a standard of living unmatched in history ?
America's free market